Because of its excellent impact resistance in addition to excellent moldability, a styrene resin has found wide application in many fields such as automobile parts, household appliance and OA (office automation) equipment parts. However, the styrene resin has restricted usage due to its flammability.
A known method for flame-retarding the styrene resin is to incorporating a halogen, phosphorus or inorganic flame retardant in the styrene resin. This method can attain flame retardation to some extent. However, the use of a halogen flame retardant disadvantageously causes environmental hazard. The use of a phosphorus or inorganic flame retardant is not satisfactory in the resulting impact strength, melt flowability and heat resistance. Further, a non-volatile organic phosphorus compound can cause staining of mold, i.e., so-called mold deposit during molding, reducing the productivity. The mold staining may be transferred to molded products, causing stress crack thereof. Thus, the industrial use is restricted.
As an approach for improving the volatility there is disclosed a resin composition for laminate comprising a phenolic resin and a specific monomeric alkyl-substituted phosphate (JP-A-1-95149 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-1-242633, JP-A-1-193328). The flame retardants disclosed in these documents apply to thermosetting resins. Thus, these flame retardants are not those for the styrene resin of the present invention.
An antistatic agent comprising a sulfonate and a phosphate such as dinonylphenyl phenylphosphate (JP-A-3-64368) and a lubricant comprising a polyol ester and a triaryl phosphate such as bisnonylphenyl phehylphosphate (U.S. Pat. No. 4,780,229) are disclosed. However, these compounds disclosed in these documents are not flame retardants and differ essentially from the present invention.
There have been known a resin composition comprising a polycarbonate, an ABS resin, a halogenated phosphate and a polytetrafluoroethylene (WO9106598), a resin composition comp-rising a polycarbonate, an AAS resin, a phosphate and a polytetrafluoroethylene (EP534297), a resin composition comprising a polycarbonate, an ABS resin, a phosphate and a polytetrafluoroethylene (DE4309142), a resin composition comprising a polycarbonate, an ABS resin, an aromatic phosphate and a metal salt of aromatic sulfinic acid (JP-A-6-299060), a resin composition comprising a polycarbonate, a polyester polycarbonate, an ABS resin, a phosphate and a polytetrafluoroethylene (EP482451), and a resin composition comprising a polycarbonate, an ABS resin, a phosphate and a polycarbonate-siloxane block copolymer (DE4016417). The phosphate to be incorporated in the foregoing polycarbonate resin composition comprises no phosphate having a specific substituent and thus exhibits a poor balance between non-volatility and flame retardance.
Further, there have been disclosed a flame retardant comprising a phosphate having a phenyl group, an isopropylphenyl group and a C.sub.4-2 alkyl-substituted phenyl group (JP-A-2-792 corresponding to EP324716), a flame retardant resin comprising a polyphenylene ether, a styrene resin and tris(isopropylphenyl)phosphate (JP-A-1-48844), and a functional fluid composition comprising a polystyrene, t-butylphenyl phenylphosphate and a polyol ester (U.S. Pat. No. 4,645,615). The total number of carbon atoms in the substituents in the phosphate of these documents on the number average falls below 12 based on the definition in the present invention described later. Thus, these compounds are insufficient in non-volatility.
The expression "C.sub.x-y alkyl" and the like used herein means "alkyl having from x to y carbon atoms" and the like.
Further, there has been disclosed a flame retardant resin composition comprising a phosphate wherein the substituents R.sub.1, R.sub.2 and R.sub.3 in formula (I) of the present invention described later each represent an aromatic hydrocarbon, such as tris(4-phenylphenyl)phosphate and tris(benzylphenyl)phosphate (DE4016417, EP534297, EP534297). The flame retardant comprising such a phosphate exhibits an excellent heat resistance but a poor melt flowability and flame retardance.
As approaches for flame-retarding the styrene resin there have been disclosed a flame retardant resin composition comprising a polyphenylene ether, a styrene resin, a metal salt of phosphoric acid and a phosphate such as tris(nonylphenyl)phosphate (JP-A-63-305161), a polyphenylene ether resin composition comprising a polyphenylene ether and a high molecular weight polyethylene as essential components, and optionally a phosphate such as tris(nonylphenyl)phosphate (EP550204), and a flame retardant resin composition comprising an aromatic polycarbonate, an ABS resin, an AS resin, a phosphate such as tris(nonylphenyl)phosphate, an aromatic sulfonate and a fibrous reinforcement (JP-A-6-299060). The resin compositions disclosed in the foregoing three documents comprise a phosphate such as tris(nonylphenyl)phosphate and thus exhibit a low flame retardance. These resin compositions exhibit a remarkably reduced heat resistance when a large amount of the foregoing phosphate is incorporated therein in an attempt to enhance the flame retardance thereof. Further, these documents do not disclose the fact that the combination of tris(nonylphenyl)phosphate, bis(nonylphenyl)phenylphosphate and nonylphenyl diphenylphosphate in predetermined proportions provides remarkable improvements in the balance of flame retardance, melt flowability, heat resistance, impact strength and water-resistant gloss retention.
As a further approach for flame-retarding the styrene resin there has been disclosed a process for the preparation of a triester phosphate comprising a hydrocarbon group selected from the group consisting of C.sub.4-22 alkyl group, C.sub.12-22 alkenyl group, phenyl group and C.sub.7-15 alkylphenyl group (alkyl moiety has from 1 to 9 carbon atoms) (JP-A-3-294284). The document not only differs from the present invention in that it relates to a preparation process but also neither discloses nor suggests the fact that the use of a specific substituent-containing monomeric aromatic phosphate provides a remarkable improvement in the continuous moldability (non-volatility) while keeping a styrene resin in particular flame retardant.
A monomeric phosphate comprising a plurality of isopropyl groups and a flame retardant composition comprising the same are disclosed (GB2027712 corresponding to US4370281 and JP-B-63-61313) (The term "JP-B" as used herein means an "examined Japanese patent publication") The total number of carbon atoms in the substituents in the phosphate of these documents is as large as from 6 to 47 based on the definition in the present invention. Further, these documents do not disclose the fact that only the substituent having a specific total number of carbon atoms on the number average can give a sufficient balance between flame retardance and non-volatility. Moreover, these documents do not refer to the fact that the incorporation of the specific substituent of the present invention can provide an enhancement of flame retardance, particularly dripping flame retardance. Further, the flame retardant according to these patents comprise a plurality of isopropyl group as substituents and thus not only exhibits too high a viscosity to be easily handled but also exhibits too low a light resistance to be put into practical use.